Artificial joints, such as knee and hip socket replacements, are frequently implanted in the body to repair or replace damaged or diseased joints. In order to achieve a successful implant, the bone adjacent to the joint must first be cut and shaped in a configuration that is geometrically reciprocal to the shape of the implant, Typically, surgeons cut with a saw blade attached to a motorized surgical handpiece that propels the blade in a variety of directional or bi-directional motions.
In most joint replacement surgery, the fit between the bone surface and the replacement must be very precise, often within tolerances of a few thousands of an inch. Virtually all surgeons use a cutting block to hold captive or guide a blade along a reference cutting surface along one or more sides of the cutting block. The reference cutting surface assures that the cutting plane will be extended to and through the bone by helping guide the blade on its path through the bone.
Although widely used, known cutting blocks and surgical methods based on the use of known cutting blocks suffer from several serious problems. A commonly encountered problem is systemic toxicity following surgery. Standard surgical cutting blocks are fabricated from various grades of stainless steel that are quickly eroded by the high speeds at which most surgical blades operate. The result of such erosion is the production of a slurry, commonly referred to as "sludge," in and near the operation site. The sludge contains the various elements present within the steel alloy of both the cutting block and the surgical saw blade. A number of metals often found in stainless steel alloys, most notably chrome and nickel, are left behind in the joint and eventually make their way throughout the patient's body. Nickel is particularly toxic and is a known carcinogen. In a recent study, Sunderman et al. (1989) report that nickel concentrations in patients having joint replacement surgery rose 11 fold in the 1 to 2 days following surgery, as compared with pre-operative levels.
Aside from the problem of toxic sludge, erosion of the stainless steel cutting blocks quickly causes fretting of the reference cutting surface, thereby destroying the ability of the cutting block to provide a precise reference plane during surgery. In most applications, tolerances of a few thousandths of an inch are lost after 5 to 10 minutes of cutting, thereby forcing the surgeon to replace the cutting block (often impractical during surgery) or accept a less precise cut. Unfortunately, the failure to provide a precise alignment along the surface contact between the prosthesis and the remaining bone can result in post-operative bone degradation, infection and joint failure.
Another serious problem associated with known cutting blocks is the heat of friction created during surgery. Although heat is generated by the frictional interaction of the saw blade and the bone, a substantial amount of heat is nevertheless generated by frictional contact between the saw blade and the cutting block. It is well known that damage to bone tissue begins after bone temperature exceeds 50.degree. C. and that irreparable damage takes place after temperatures exceed 70.degree. C. for three or more minutes. Known cutting devices and methods can generate temperatures in excess of 50.degree. C. or even 70.degree. C.
In view of the foregoing, there is a clear need for a surgical cutting block and method of use that substantially reduces or eliminates delivery of toxic elements to a patient as a by-product of erosion of the cutting block. There is also a need for a cutting block with superior hardness that is capable of retaining its original configuration without unacceptable fretting during prolonged use. A further need is for a cutting block and blade combination that has a relatively low coefficient of friction during operation, thereby reducing blade heating and bone tissue degradation.